<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #box1{
            font-size: 16px;
        }
        #box2{
            font-size:12pt; /*12pt=16px*/
        }
        #box3{
            font-size:1pc; /*1pc=12pt*/
        }
        #box4{
            font-size:1em; /*1em=16px*/
        }
        #box5{
            font-size:100%; /*16px=100%*/
        }
    </style>
</head>
<body>
<div id="box1">HTML5教程</div>
<div id="box2">HTML5教程</div>
<div id="box3">HTML5教程</div>
<div id="box4">HTML5教程</div>
<div id="box5">HTML5教程</div>
</body>
</html>